Mechanical properties and durability of alkali-activated steel slag–blastfurnace slag cement

Alkali-activated cement (AAC) is either clinker-less or free, and it is also environmentally friendly due to its low carbon footprint and wide range sources. Industrial wastes, like steel slag and blastfurnace slag, usually have latent hydraulic reactivity, and can be used as precursors of AAC. Both clinkerless and clinker-free AAC were prepared from the mixture of steel slag and blastfurnace slag by using water glass as an activator, and four different recipes which satisfied the strength requirement of 42.5R Portland cement were obtained. Each recipe of AAC exhibited better resistance to sulfate attack and frost attack than Portland cement. AAC showed huge drying shrinkage, but it was equivalent to that of Portland cement as steel slag content increased to 40%. The AAC also had quite low risk of alkali-aggregate reaction. Microstructure analysis showed that the major products were calcium silicate hydrate (C–S–H), calcium aluminosilicate hydrate (C–A–S–H) and zeolite-like phases. Ettringite was also detected in the binder when gypsum was contained in the precursors.